Stabilised aerial

ABSTRACT

A lightweight aerial mast for electromagnetic waves is provided with a planar reflector fixed to the top of the mast for reflecting waves onto a planar reflector near the ground, which in turn reflects the waves to a parabolic reflector at whose focus there is a horn aerial. The parallelism of the two planar reflectors is made independent from the bending of the mast due to a connection between these two reflectors provided by three parallel wires of equal lengths which are held taut.

I 22 l ned? United States Patent Tocquec Sept. 5, 1972 [54] STABILISED AERIAL [72.1 iYltqfil I is seli le az ass sfli [73]- Assignee: Compagnie Generale DElectricite,

M 'Paris, France July 22, 1970 21 Appl.No.: 57,266

' 301 Foreign Application Priority Data July 23, 1969 France ..o92s17o s21 U.S.Cl. ..343/781, 343/836, 343/337, 343/890 3 51 lnt.Cl. ..H01q1/12,l-I01q 19/10 [58] Field of Search 343/781, 874, 915, 892, 878, 343/879, 885, 886, 755, 758, 761, DIG. 1; 350/301 [5 6] References Cited UNlTED STATES PATENTS 1 3855 18. 1 1 59 1 jo er, $3 0M 2,5 10,059 2,665,383 1/1954 Marie ..343/755 Primary Examiner-Eli Lieber man Assistant Examiner-Marvin Nussbaum Attorney-Sughrue, Rothwell, Mion, Zinn & Macpeak ABSTRACT A lightweight aerial mast for electromagnetic waves is provided witha planar reflector fixed to the top of the mast for reflecting waves onto a planar reflector near the ground, which in turn reflects the waves to a parabolic reflector at whose focus there is a horn aerial. The parallelism of the two planar reflectors is made independent from the bending of the mastdue to a connection between these two reflectors provided by three parallel wires of equal lengths which are held 9 Claims, 1 Drawing Figure 6/1950 Black "52/40 STABILISED AERIAL The present invention concerns aerials for very high frequency electromagnetic radiation and including reflectors. More particularly, it concerns aerials in which these reflectors are mounted on a structure with relatively low rigidity.

In radio telecommunications between ground stations, it is necessary to reduce to a minimum any movements of the aerial, caused by vegetation for example, especially by trees. For this reason, it is common to mount a reflector on a mast which rises above the surrounding vegetation. It has been proposed to use a plane reflector arranged at an angle of 45 to the ground. Horizontally propagated waves striking the mirror are reflected downwards on to a second reflector, this reflector being parabolic so as to concentrate the waves at its focus where there is disposed a suitable receptor element.

This parabolic mirror is easily stabilized since it is supported on the ground on a relatively small structure. The plane mirror, however, being placed at the top of the mast, suffers displacements due to the flexibility of the mast and gusts of wind. There results an instability in the lobe of the aerial and a loss in gain which may be considerable. While it is possible to increase the rigidity of the mast, particularly by the use of a sufficient number of stays, it is not possible to reduce these variations in the gain of the aerial to negligible proportions, by reducing flexing of the mast, without an increase in the weight of the mast structure which would be unacceptable in most applications.

The present invention is intended to provide an aerial which is light and which has a directionally stable principal lobe.

In accordance with the invention there is provided an aerial comprising a first reflector mounted at the top of a mast and a second reflector disposed at the foot of the mast, the first and second reflectors being linked by ties extending between them and being so mounted that displacements of one reflector are transmitted to the other through the ties.

The aerial suitably comprises three parallel ties and has the second reflector mounted so as to be rotatable about at least two axes perpendicular to the ties.

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawing.

Referring to the drawing, an aerial comprises a light and flexible mast 2 which is maintained in position by stays 4, 6, 8, l0, l2, 14. A triangular support frame 16 at the top of the mast 2 carries a first plane reflector 18. A second plane reflector 20 is disposed at the foot of the mast, and the two reflectors are linked by parallel ties 22, 24 and 26 of the same length. A parabolic reflector 258 is mounted on the mast 2 opposite the reflector 20, and has a horn aerial (not shown) at its focus, connected to a transmitter-receiver system not shown). The reflector 20 is supported on frames 30, 32 and 34. The frames elastically support the reflector 20 and dampen any vibrations. The center of the reflector 20 remains in a substantially fixed position.

The ties 22, 24, 26 are substantially vertical, the reflector 20; being displaced slightly from the position directly below the reflectorlfl to provide a suitable clearance between itself and the reflector 28. The ties 22, 24, 26 are equally spaced around the reflector rims, and the reflectors are inclined at 45 to a horizontal plane.

When the aerial acts as a receiver aerial, horizontally propagated waves from the appropriate direction are reflected downwardly from the reflector 18 to the reflector 20, whence they are reflected to the reflector 28 and its horn aerial.

The reflector 20 is mounted so as to be rotatable about any axis perpendicular to the ties 22, 24, 26, so that when a gust of wind alters the inclination of the reflector 18, the movements of the reflector 18 are transmitted to the reflector 20 through the ties 22, 24, 26; the movements of the two reflectors are identical, so that the reflectors remain parallel. The incident waves are thus reflected horizontally from the reflector 20 to reflector 28, even though the inclinations of the two plane reflectors have changed. There is thus no significant change in the gain of the aerial, provided that the reflector 18 is sufficiently large for substantially all of the waves reflected downwardly from the reflector 18 to fall on the reflector 20.

A particular aerial such as just described, for operation at a frequency of 13 GHz, has a parabolic reflector 28 of 60 centimeters diameter, with horizontal axis. The reflector 20 is elliptical, with a smaller axis slightly greater than 60 centimeters, so as to be able to reflect all waves from the parabolic reflector 28. The mast height is 15 meters, but evidently depends on the site of the aerial and the height of the surrounding vegetation. The reflector 20 may be made larger than the reflector l3, and even slightly concave to correct for the deformations of the wave fronts between the reflectors 18 and 20. In this particular example, the concavity is l centimeter.

As previously indicated, the reflector 18 must be sufficiently large to ensure all waves reflected from it land on the reflector 20. It is only for the sake of clarity that these reflectors are shown the same size in the drawing.

The parabolic reflector 28 is suitably provided with means for adjusting its alignment, so that it can be adjusted for optimum operation once the aerial is erected.

The stays 10, 12, 14 are arranged so as to minimize the possibility of the mast 2 rotating about its axis.

While three ties 22, 24, 26 are shown in the accompanying drawing, in certain applications it may be convenient to use more or less.

What is claimed is: r

1. An aerial comprising a mast; a first reflector connected to said mast; a second reflector located adjacent the base of said mast; the first and second reflectors,

being substantially planar; tie means linking said first and second reflectors, and means for mounting said first and second reflectors so that angular displacements of one reflector are transmitted to the other by said tie means.

2. An aerial as claimed in claim 1, where said tie means comprises two ties and wherein said second reflector is mounted parallel to said first reflector and is rotatable about at least one axis inclined to the plane of said ties.

3. An aerial as claimed in claim 1, where said tie means comprises three parallel ties and wherein said second reflector is mounted so as to be rotatable about at least two axes perpendicular to said ties.

4. An aerial as claimed in claim 1 wherein said first reflector is rigidly attached to the mast at a distance above said second reflector.

5. An aerial as claimed in claim 4 further comprising a parabolic reflector and wherein said second reflector is situated opposite and co-operates with said parabolic reflector.

6. An aerial as claimed in claim 5, wherein said located adjacent the base of said mast; tie means linking said first and second reflectors and means for mounting said first and second reflectors so that angular displacements of one reflector are transmitted to the other by said tie means.

9. An aerial comprising a mast; a first reflector connected to said mast; a second reflector located adjacent the base of said mast; the first and second reflectors being elliptical; tie means linking said first and second reflectors, and means for mounting said first and second reflectors so that angular displacements of one reflector are transmitted to the other by said tie means. 

1. An aerial comprising a mast; a first reflector connected to said mast; a second reflector located adjacent the base of said mast; the first and second reflectors being substantially planar; tie means linking said first and second reflectors, and means for mounting said first and second reflectors so that angular displacements of one reflector are transmitted to the other by said tie means.
 2. An aerial as claimed in claim 1, where said tie means comprises two ties and wherein said second reflector is mounted parallel to said first reflector and is rotatable about at least one axis inclined to the plane of said ties.
 3. An aerial as claimed in claim 1, where said tie means comprises three parallel ties and wherein said second reflector is mounted so as to be rotatable about at least two axes perpendicular to said ties.
 4. An aerial as claimed in claim 1 wherein said first reflector is rigidly attached to the mast at a distance above said second reflector.
 5. An aerial as claimed in claim 4 further comprising a parabolic reflector and wherein said second reflector is situated opposite and co-operates with said paRabolic reflector.
 6. An aerial as claimed in claim 5, wherein said parabolic reflector is attached to said mast.
 7. An aerial as claimed in claim 1 wherein said second reflector is larger than said first reflector.
 8. An aerial comprising a mast; a first reflector connected to said mast; a slightly concave second reflector located adjacent the base of said mast; tie means linking said first and second reflectors and means for mounting said first and second reflectors so that angular displacements of one reflector are transmitted to the other by said tie means.
 9. An aerial comprising a mast; a first reflector connected to said mast; a second reflector located adjacent the base of said mast; the first and second reflectors being elliptical; tie means linking said first and second reflectors, and means for mounting said first and second reflectors so that angular displacements of one reflector are transmitted to the other by said tie means. 